China solar greenhouses, built on south facing slopes, are an underdocumented innovation. A recent study looks at their history and suggests additional ways to improve them. (Source: Energy Bulletin)

Chinese innovation starting to show itself on the world scene

One
perpetual criticism of China, the world’s second largest economic super-power,
is that its lacks the innovation found in the U.S., Japan, or European Union.
Perhaps that is a bit of an exaggeration, however.

A great deal of innovation in China has not been absent, but has merely gone
undocumented until late.

Take China's advanced solar green houses, which were designed more than 20
years ago. In a new peer-review study [abstract]
published in the journal ASHS (American Society for Horticultural Science)
HortTech, researchers at the China Agricultural University in Beijing have
detailed how the Chinese innovation -- built on slopes -- offer great savings
in power costs and emissions.

It's not surprising that China might know a thing or two about efficient
growing. It has to feed the world's largest population -- over 1.3
billion people, today. That's no easy task. To sustain the
population, China had to figure out how to grow crops cheaply and effectively
in the winter. To do that it created the slope greenhouse design.

The greenhouses studied lie in regions north of Huai River and the Beijing
area. Like any greenhouses, their feasibility as winter growing sites
relies on the temperature at the site and the amount of sunlight during the
winter.

What is unique about the Chinese design is that they use the slope to provide a
degree of natural insulation, while optimizing solar absorbance. The back
wall is situated directly into the slope and side walls jut out of the slope on
a flattened plot of land. On top, a thin roof is built. This gives
way to the sloping transparent curved roof/front wall, the first thing you see
when looking at the greenhouse from outside.

The greenhouses are constructed using simple materials. A frame made of
bamboo, metal, or a combination of both supports the curved glass wall.
The transparent wall is formed of an insulating sheet and plastic film.

While the greenhouses have numerous advantages -- "energy savings, reduced
pollution, and improved economic development" -- they also have
disadvantages, which the authors note. Namely, weather conditions can
limit sunlight, causing growing problems. The greenhouses are heavily
reliant on sun and weather conditions.

Still their cheap, efficient, easy to construct design has been an alluring
innovation for other nations, situated between the applicable 32°N and
43°N latitudes. Among the countries implementing them are Japan,
Korea, and Russia. The greenhouses are used to grow warm-weather crops
like tomatoes and cucumbers.

The report author, Zhen-Xian Zhang, speculates on how to improve upon the
tried-and-true design, stating [press
release], "Innovation and optimization of the greenhouse structure
needs to continue. More work needs to be done on gutter-connected,
double-arched, and semi-underground greenhouses. New wall insulation materials
need to be developed to reduce the thickness of the wall while improving its
insulation efficiency and expanding space utilization. The solar greenhouse has
a very bright future, especially given the amount of concern over the global
energy crisis and climate change. Additionally, significant energy savings can
be realized from switching to solar greenhouses. We hope this technology can be
applied to regions of similar climate to help reduce energy consumption and CO2
emissions."

Professor Zhang also suggested breeding special hybrid crops optimized for
growth in the occasionally adverse conditions of the winter greenhouse.
Such crops might resist brief chills and add already more utility to this
tested design.

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